Deck 13: Vibrations and Waves: Part A

Question 1

In the afternoon,the decibel level of a busy freeway is 80 dB with 100 cars passing a given point every minute.Late at night,the traffic flow is only 8 cars per minute.What is the late-night decibel level?

A) 77 dB
B) 74 dB
C) 70 dB
D) 69 dB

Answer 1

69 dB

Question 2

The density of a certain solid is 7.2 × 10³ kg/m³,and its Young's modulus is 8.0 × 10¹⁰ N/m².What is the speed of sound in this material?

A) 1.1 × 10⁷ m/s
B) 5900 m/s
C) 3700 m/s
D) 3300 m/s

Answer 2

3300 m/s

Question 3

What is the intensity level of a sound with intensity of 5.0 × 10−¹¹ W/m²? (I₀ = 10−¹² W/m²)

A) 74 dB
B) 54 dB
C) 17 dB
D) 27 dB

Answer 3

17 dB

Question 4

Material 1 has Young's modulus Y1 and density ρ1,material 2 has Young's modulus Y₂ and density ρ₂,and material 3 has Young's modulus Y3 and density ρ​₃.If Y1 > Y₂ > Y3 and if ρ1 < ρ2 < ρ​3,which material has the highest speed of sound?

A) material 1
B) material 2
C) material 3
D) They could all have equal speeds of sound.

Question 5

The frequency separating audible waves and ultrasonic waves is considered to be 20 kHz.What wavelength in air at room temperature is associated with this frequency? (Assume the speed of sound to be 340 m/s. )

A) 0.59 cm
B) 1.7 cm
C) 34 cm
D) 55 cm

Question 6

If one-half of the members of a symphony orchestra are absent because of head colds,thus reducing the overall intensity of sound by 50%,what will be the reduction in the decibel level?

A) 5 dB
B) 3 dB
C) 48 dB
D) 1.7 dB

Question 7

A sound wave coming from a tuba has a wavelength of 0.674 m and travels to your ears at a speed of 345 m/s.What is the frequency of the sound you hear?

A) 512 Hz
B) 1/517 Hz
C) 230 Hz
D) 1/230 Hz

Question 8

Which of the following best describes a sound level of intensity 10^-6 W/m²?

A) extremely loud
B) about that of a power mower
C) normal conversation
D) like a whisper

Question 9

If the distance between a point sound source and a dB detector is increased by a factor of 10,what will be the reduction in intensity level?

A) 10 dB
B) 16 dB
C) 20 dB
D) 32 dB

Question 10

A sound wave in air has a frequency of 515 Hz and a wavelength of 0.68 m.What is the air temperature?

A) -18°C
B) 32°C
C) 15°C
D) 27°C

Question 11

A series of ocean waves,2.5 m between crests,move past at 2.0 waves/s.Find their speed.

A) 2.5 m/s
B) 5.0 m/s
C) 8.0 m/s
D) 10 m/s

Question 12

If the intensity of a sound is increased by a factor of 1000,how is the decibel level changed? The new decibel level will be:

A) three units greater.
B) ten times greater.
C) thirty times greater.
D) twenty units greater.

Question 13

How far away is a lightning strike if you hear the thunderclap 2.00 s after you see the lightning bolt strike? (v_sound = 340 m/s,v_light = 3 × 10⁸ m/s)

A) 113 m
B) 340 m
C) 680 m
D) 1020 m

Question 14

Which of the following ranges corresponds to the shortest wavelengths?

A) infrasonic
B) audible
C) ultrasonic
D) All have the same wavelengths.

Question 15

A chamber that can be filled with different gases has placed in it a source of sound that in air produces a frequency of 200 Hz and a microphone to pick up the sound for frequency analysis.First the chamber is filled with helium (speed of sound 1 000 m/s at room conditions),then the helium is replaced with oxygen (speed of sound 330 m/s at room conditions),and then finally the helium is replaced with carbon dioxide (speed of sound 269 m/s at room conditions).In which gas is the highest frequency of sound found by the microphone during this experiment?

A) helium
B) oxygen
C) carbon dioxide
D) They all have the same frequency of sound.

Question 16

Doubling the distance between sound source and a listener will change the intensity,as detected by the listener,by what factor?

A) 4
B) 2
C) 1/2
D) 1/4

Question 17

Doubling the power output from a speaker emitting a single frequency will result in what increase in loudness?

A) 0.33 dB
B) 3.0 dB
C) 4.8 dB
D) 9.0 dB

Question 18

The speed of sound at 0°C is 331 m/s.What is the speed of sound at 32°C? (0°C = 273 K)

A) 346 m/s
B) 356 m/s
C) 343 m/s
D) 350 m/s

Question 19

Material 1 has Young's modulus Y₁ and density ρ​₁,and material 2 has Young's modulus Y​₂ and density ρ₂.If Y₁ is 30% more than Y​₂ and ρ​₁ is 30% less than ρ₂,which material has the higher speed of sound and how much higher is it?

A) Material 1 has a speed of sound more than 35% higher than material 2.
B) Material 1 has a speed of sound 30% higher than material 2.
C) Material 2 has a speed of sound more than 80% higher than material 1.
D) Material 2 has a speed of sound 30% higher than material 1.

Question 20

What sound level change most nearly corresponds to a factor of three change in intensity?

A) 0.5 dB
B) 2 dB
C) 3 dB
D) 5 dB

Question 21

Two loudspeakers are placed facing each other and driven by the same source at 680 Hz.A listener is positioned between the two speakers on the line separating them,thus creating a constructive interference at the listener's ear.If one of the speakers is gradually pushed toward the listener,how far must it be moved to repeat the condition of constructive interference at the listener's ear? (The speed of sound = 340 m/s. )

A) 0.13 m
B) 0.25 m
C) 0.50 m
D) 1.00 m

Question 22

By what amount does the sound intensity decrease when the distance to the source triples?

A) 9.0 dB
B) 9.5 dB
C) 6.0 dB
D) 3.5 dB

Question 23

A vibrating guitar string emits a tone simultaneously with one from a 500-Hz tuning fork.If a beat frequency of 4 Hz results,what is the frequency of vibration of the string?

A) 2500 Hz
B) 496 Hz
C) 504 Hz
D) Either choice B or C is valid.

Question 24

If two adjacent frequencies of an organ pipe closed at one end are 500 Hz and 700 Hz,what is the length of the organ pipe? (v_sound = 340 m/s)

A) 0.85 m
B) 1.25 m
C) 1.50 m
D) 1.70 m

Question 25

What is the lowest frequency that will resonate in an organ pipe 1.00 m in length,closed at one end? The speed of sound in air is 340 m/s.

A) 42.5 Hz
B) 85.0 Hz
C) 170 Hz
D) 680 Hz

Question 26

A tuning fork is sounded above an adjustable length resonating tube (one end closed),which resonates at a length of 0.250 m and again at 0.750 m.What is the frequency of the fork when the speed of sound is taken to be 340 m/s?

A) 340 Hz
B) 680 Hz
C) 1020 Hz
D) 170 Hz

Question 27

A tuning fork is sounded above an adjustable length resonating tube (one end closed),which resonates at a length of 0.250 m and again at 0.750 m.If the tube length were extended further,at what point will the tuning fork again create a resonance condition?

A) 1.75 m
B) 1.50 m
C) 1.25 m
D) 1.00 m

Question 28

A sound intensity of 70 dB is observed at a distance d from the source of sound.What sound intensity would be observed at a distance 2d from the source?

A) 68 dB
B) 67 dB
C) 64 dB
D) 62 dB

Question 29

Two loudspeakers are placed facing each other and driven by the same source at 680 Hz.A listener is positioned between the two speakers on the line separating them,thus creating a constructive interference at the listener's ear.What minimum distance would one of the speakers be moved back away from the listener to produce destructive interference at the listener's ear? (The speed of sound = 340 m/s. )

A) 0.13 m
B) 0.25 m
C) 0.50 m
D) 1.00 m

Question 30

A source of sound has an intensity I​₁ and when its sound level is measured at a fixed distance the value found is 70 dB.The source then has its intensity increased to I​₂ and when its sound level is measured at the same distance the value found is 96 dB.What is the ratio ​I​₂/​I​₁?

A) 26
B) 400
C) 600
D) 14

Question 31

Two vibrating tuning forks,held side by side,will create a beat frequency of what value if the individual frequencies of the two forks are 321 Hz and 326 Hz,respectively?

A) 323.5 Hz
B) 647 Hz
C) 5 Hz
D) 2.5 Hz

Question 32

Two tuning forks sounding together result in a beat frequency of 3 Hz.If the frequency of one of the forks is 512 Hz,what is the frequency of the other?

A) 509 Hz or 515 Hz
B) 105 Hz
C) 518 Hz or 506 Hz
D) 85 Hz

Question 33

A very loud train whistle has an acoustic power output of 80 W.If the sound energy spreads out spherically,what is the intensity level in dB at a distance of 100 meters from the train? (I₀ = 10−¹² W/m²)

A) 78.3 dB
B) 88.0 dB
C) 92.8 dB
D) 95.0 dB

Question 34

What is the next harmonic frequency over the fundamental for an organ pipe 1.50 m in length,closed at one end? The speed of sound in air is 340 m/s.

A) 227 Hz
B) 170 Hz
C) 113 Hz
D) 56.7 Hz

Question 35

A flute behaves like a tube open at both ends.If its length is 70.0 cm,and the speed of sound is 340 m/s,what is its fundamental frequency in Hz?

A) 121 Hz
B) 159 Hz
C) 243 Hz
D) 260 Hz

Question 36

The intensity level of sound 30 m from a jet airliner is 120 dB.At what distance from the airplane will the sound intensity level be a tolerable 100 dB? (Assume spherical spreading of sound. )

A) 60 m
B) 90 m
C) 300 m
D) 400 m

Question 37

A train station bell gives off a fundamental tone of 1000 Hz as the train approaches the station at a speed of 20.0 m/s.If the speed of sound in air is 335 m/s,what will be the apparent frequency of the bell to an observer riding the train?

A) 1060 Hz
B) 1070 Hz
C) 943 Hz
D) 940 Hz

Question 38

A phase difference of 480° corresponds to what wavelength difference?

A) 3λ
B) 3λ/2
C) 3λ/4
D) 4λ/3

Question 39

You stand by the railroad tracks as a train passes by.You hear a 950-Hz frequency when the train approaches,which changes to 820 Hz as it goes away.How fast is the train moving? The speed of sound in air is 340 m/s.

A) 14.0 m/s
B) 20.0 m/s
C) 25.0 m/s
D) 37.8 m/s

Question 40

A 2.00-m long organ pipe is open at one end and closed at the other.Its fundamental tone has wavelength:

A) 8.00 m.
B) 4.00 m.
C) 2.00 m.
D) 1.00 m.

Question 41

When one note is above another note by an octave,the frequency of the higher pitch note is double that of the lower pitch note.The word octave may make you think that there are 8 steps from the lower note to the one an octave above.But wait! How many steps are there on a piano from middle C to the next C above? Each key is a step.If each next key is a step,how many are there? Middle C is a white (W)key and the next note above is a black (B)key.Starting at middle C on the piano the sequence of key we go through to get to high C,is BWBWWBWBWBWW,the last key being high C.Count 'em.That's 12 steps.If the multiplying factor of the frequency for the next step is the same for each step,what is that multiplying frequency? All you need is given in this problem statement.

A) 10^1/12
B) 12^1/8
C) 2^1/8
D) 2^1/12

Question 42

A plane is traveling at Mach 0.980 through air at a temperature of 0°C.What is the plane's speed? (Speed of sound at 0°C is 331 m/s. )

A) 314 m/s
B) 324 m/s
C) 348 m/s
D) Mach number is undefined at 0°C.

Question 43

A sound source of frequency 1000 Hz moves at 40.0 m/s toward a listener who is at rest.What is the apparent frequency heard by the listener? (speed of sound = 340 m/s)

A) 853 Hz
B) 872 Hz
C) 1130 Hz
D) 1170 Hz

Question 44

A bat,flying at 3.00 m/s toward a wall,emits a chirp at 50.0 kHz.If the wall reflects this sound pulse,what is the frequency of the echo received by the bat? (v_sound = 340 m/s)

A) 51.5 kHz
B) 51.2 kHz
C) 40.8 kHz
D) 50.9 kHz

Question 45

While standing at a crosswalk,you hear a frequency of 540 Hz from an approaching police car.After the police car passes,its frequency is 480 Hz.What is the speed of the police car? (speed of sound = 340 m/s)

A) 13.1 m/s
B) 17.4 m/s
C) 20.0 m/s
D) 26.2 m/s

Question 46

Two cars,one in front of the other,are traveling down the highway at 25 m/s.The car behind sounds its horn,which has a frequency of 540 Hz.What is the frequency heard by the driver of the lead car? (v_sound = 340 m/s)

A) 463 Hz
B) 540 Hz
C) 579 Hz
D) 500 Hz

Question 47

A 500-Hz whistle is moved toward a listener at a speed of 10.0 m/s.At the same time,the listener moves at a speed of 20.0 m/s in a direction toward the whistle.What is the apparent frequency heard by the listener? (The speed of sound is 340 m/s. )

A) 473 Hz
B) 485 Hz
C) 533 Hz
D) 545 Hz

Question 48

The Doppler shift of ultrasonic waves can measure the speed of blood in an artery.If the frequency of the stationary source is 100 kHz and the reflected sound has a Doppler shift of 300 Hz,what is the blood flow speed? (The speed of sound inside the body is 1500 m/s. )

A) 1.0 m/s
B) 1.5 m/s
C) 2.2 m/s
D) 3.3 m/s